A conventional hearing aid or listening device can include both a microphone and a telecoil for receiving inputs. The microphone picks up acoustic sound waves and converts the acoustic sound waves to an audio signal. That signal is then processed (e.g., amplified) and sent to the receiver (or “speaker”) of the hearing aid or listening device. The speaker then converts the processed signal to an acoustic signal that is broadcast toward the eardrum.
On the other hand, the telecoil picks up electromagnetic signals. The telecoil produces a voltage over its terminals when placed within an electromagnetic field, which is created by an alternating current of an audio signal moving through a wire. When the telecoil is placed near the wire carrying the current of the audio signal, an equivalent audio signal is induced in the telecoil. The signal in the telecoil is then processed (e.g. amplified) and sent to the receiver (or “speaker”) of the hearing aid for conversion to an acoustic signal.
Similarly, a typical telecommunication system consists of a combination of a receiver and a microphone in one housing. The signal from the microphone to the receiver is amplified before the receiver broadcasts the acoustic signal toward the eardrum.
In a typical balanced armature receiver, the housing is made of a soft magnetic material, such as a nickel-iron alloy. The housing serves several functions. First, the housing provides some level of sturdiness. Second, the housing also provides a structure for supporting the electrical connections. Third, the housing provides both magnetic and electrical shielding. Lastly, the housing may provide acoustical and vibrational isolation to the rest of the hearing aid.
In either a telecommunication system or a hearing aid, the gain introduced between the microphone and the receiver may result in feedback problems. The vibration or acoustical radiation of the receiver creates an undesirable feedback signal that is received by the microphone. Furthermore, in a hearing aid with a telecoil, a magnetic feedback signal may create feedback problems.
In both hearing aids and telecommunication devices, it is important for the receiver to be configured to withstand the forces associated with handling without damaging the housing. These forces can arise through the assembly of the receiver within a hearing aid, such as when a receiver is grasped with tweezers while it is being positioned or when force is placed on the housing when electrical connections are being made. Disfiguring the housing can easily occur because the housing material is thin and has a low hardness. One common type of damage is a simple dent that can occur in the housing. Dents can affect not only the electronics within the housing, but they can affect the performance of the acoustical chambers within the receiver. Because the housing of a receiver is typically made of a case and a cover that are made by a drawing technique, dents near the interface of the case and cover can also lead to acoustic leaks at the interface. Because of the minimal thickness of the material in the housing and a minimal size of the receiver, magnetic and acoustical isolation are limited.
Thus, a need exists for a receiver having small dimensions, but which has enhanced structural integrity and electromagnetic shielding.